I would add some images of a small run-down apartment and label it The Younger Apartment. Also, you could find a picture of a child sleeping on the couch, as did ten-year-old Travis. You could add images of a chauffeur, which was Walter's job or occupation. Also, Walter drank alcohol and lost the family's money. Perhaps, you could include photos of someone drinking too much alcohol. Images of money being wasted would be ideal.
You could also find domestic or house keeping occupations. Mrs. Lena Younger and Ruth did other people's laundry and house keeping.
As for Beneatha, she was curious as to her roots as an African American. You could find some African clothing like the Nigerian dress and head band Beneatha wore.
You could also find college prep clothes that George wore. He wore white buckskin shoes.
You could find a picture of a straggly plant (a pitiful plant) like the symbolic plant that Mama kept, symbolizing that she would survive no matter the struggle:
One of the symbols in A Raisin in the Sun is Mama's straggly plant. She wants to take this to the new house, although she plans to have a much more successful garden there, because this plant 'expresses ME.' Though the plant has struggled to live and seems to lack the beauty for which it would ordinarily be valued, it is significant to Mama because it has survived despite the struggle, as her family has survived.
On a happy note, you could find a picture of a nice, new home in a nice neighborhood. This house symbolized hope for the Younger family. They were ecstatic to move into a new home of their very own.
These are some ideas, symbols and images you could put on your poster board. Hope these ideas help. Good luck with your assignment.